The present application is based on Japanese Patent Application No. 2001-134007, which is incorporated herein by reference.
The present invention relates to a gear-train coupled motor coupled with a gearbox containing a reduction gear train.
There is known a motor in which a motor unit is coupled with a gear box containing a reduction gear train. This type of motor will be referred to as a geared motor. The geared motor has widely been used in various types of devices. The motor, inter alia, a stepping motor, is used as a drive source which drives those various types of devices while controlling the devices. This type of motor is used for the focusing, zooming or the like in digital still cameras, digital video cameras, and further it has found its application in audio/video devices, office automation (OA) devices and others.
The geared motor includes a motor unit and a plurality of transmission gears for transmitting a driving force from the motor unit to the output part. In the conventional geared motor, those gears, which are located between the motor output shaft of the motor unit and the output part are spur gears. FIG. 6 is a conceptual figure showing a conventional geared motor. In FIG. 6, a gear box 52 is fixed to one end of a motor unit 51. A motor shaft is projected from one end of the motor unit 51 toward the gear box 52, and a small-diameter gear 54 is secured to the motor shaft. The gear 54 is in mesh with a gear 55. A gear 57 is in mesh with a small-diameter bevel gear 56 integral with the gear 55. A gear 59 is in mesh with a small-diameter gear 58 integral with the gear 57. The gear 59 includes a small-diameter gear 60 integral with the former. Those gears are all spur gears. Accordingly, the shafts of those gears are oriented in a direction perpendicular to the mounting surface of the motor unit 51, which is used when the gear box 52 is mounted on the motor unit. A rotational driving force is output from the small-diameter gear 60 or a rotary shaft integral with the small-diameter gear.
In the conventional geared motor, the transmission gear train consists of spur gears. All the shafts of the transmission gear train are parallel to the rotary shaft of the motor unit 51, and are arranged in the outer radial direction of the motor unit 51. Accordingly, the gear box 52 extends in a direction perpendicular to the shaft direction of the motor unit 51. In assembling the geared motor into a device, a space within the device is greatly occupied by the gear box 52 of the geared motor in the widthwise direction. This space occupation hinders the approach of making the device compact and lessens the freedom of mounting the geared motor. In connection with this, there is an approach in which the transmission gear train is disposed along an arc with its center being the motor shaft, with an intention of minimizing the expansion of the gear box 52 relative to the motor unit 51. In this approach, the gear box expands radially and equiangularly from the motor shaft. This spatial expansion also hinders the securing of the device compactness and good freedom of the geared motor mounting.
Accordingly, an object of the present invention is to provide a geared motor in which the overall width of the device is reduced by reducing the device size expansion in the width direction.
According to the present invention, there is provided a first geared motor comprising: a motor unit having an motor output shaft; a plurality of transmission gears for transmitting a driving force of the motor unit to an output part, the transmission gears being supported by transmission gear shafts; a casing which covers said motor output shaft and said transmission gears, including a pair of opposed walls opposed substantially in parallel with each other and a coupling surface being arranged substantially in parallel with said transmission gear shafts; wherein shaft supporting parts for supporting ends of the transmission gear shafts of the transmission gears, formed on said opposed walls of said casing; an insertion hole penetrating said coupling surface, and an output-side end surface of said motor unit is fastened to said coupling surface.
According to another aspect of the invention, there is provided a second geared motor comprising: a motor unit; a plurality of transmission gears for transmitting a driving force from the motor unit to the output part; wherein said transmission gears includes a first bevel gear supported by a first shaft, and a second bevel gear meshing with said first bevel gear and supported by a second shaft oriented in a direction orthogonal to said first shaft of said first bevel gear; and
at least one of said first and second bevel gears is provided with shaft support parts so that both ends of said at least one of said first and second bevel gears are supported.
In the second geared motor, a casing for accommodating a plurality of gears therein is made of resin, and the shaft support parts are formed in the casing.
In a preferred embodiment, the second bevel gear is mounted on the motor output shaft.
In another preferred embodiment, the motor output shaft of the motor unit includes a stepped part formed by making the output shaft different in diameter, and the stepped part serves as a thrust receiver for the second bevel gear.
In a further preferred embodiment, the shafts of the bevel gear and the second bevel gear are both supported at both ends thereof, and the ends of the shafts of the bevel gear and the second bevel gear, which are located close to each other, are supported by a common shaft support.